The compound (−)-Δ9-trans-tetrahydrocannabinol is the active ingredient in marijuana. It is used therapeutically as an inhalant or an oral drug for stimulation of appetite among AIDS and cancer chemotherapy patients. Tetrahydrocannabinols (THCs) can be isolated from marijuana (a mixture of leaves and flowering heads of the plant Cannabis Sativa). Alternatively, THCs can be obtained by synthetic routes, e.g. as described in WO 02/096899.
Pure (−)-Δ9-trans-tetrahydrocannabinol that has been produced synthetically and purified is unstable and is liable to degrade to products such as cannabinol (which is inactive) and Δ8-tetrahydrocannabinol (which is less potent). Although Δ8-tetrahydrocannabinol has similar activity to as (−)-Δ9-trans-tetrahydrocannabinol it is only approx. 75% as potent and also tends to degrade to other compounds including cannabinol. Dissolving the (−)-Δ9-trans-tetrahydrocannabinol in a solvent or carrier improves the stability, but it is still usual to store the solutions under refrigerated conditions, e.g. at 5° C., to prevent degradation. The present inventors have sought to improve the stability of solutions of (−)-Δ9-trans-tetrahydrocannabinol and Δ8-tetrahydrocannabinol.